This disclosure relates to the field of power tools, and more particularly to handheld power tools having an oscillating tool or blade attachments.
Oscillating power tools can be lightweight, handheld tools configured to oscillate various accessory tools and attachments, such as cutting blades, sanding discs, grinding tools, and many others. The accessory tools and attachments can enable the oscillating power tool to shape and contour workpieces in many different ways.
FIGS. 1-5 illustrate a conventional oscillating power tool 10 having a generally cylindrically shaped housing 12 and a tool head 14 located at a front end of the housing 12. As shown in FIG. 1, the housing 12 includes a handle portion 16 formed to provide a gripping area for an operator. The housing 12 is further configured to carry a power supply and a motor M that drives an eccentric motor shaft 18 which engages a spherical drive bearing 20. The housing 12 can be constructed of a rigid material such as plastic, metal, or a composite material such as a fiber reinforced polymer.
Turning now to FIG. 2, the eccentric motor shaft 18 includes an eccentric pin 19 and the spherical drive bearing 20 includes ball bearings 21 positioned around the eccentric pin 19 and contained within an outer race 23. As the eccentric motor shaft 18 rotates, the eccentric pin 19 moves in a circular path or orbit about a longitudinal axis S of the shaft 18. The ball bearings 21 translate this rotational motion to the outer race 23 and the outer race 23 moves in the same circular path about the longitudinal axis S.
Returning now to FIG. 1, the tool head 14 is configured to support an output spindle 22 having a tool accepting portion 24 configured to accept a number of different tools or tool accessories, such as, for example, scraping tools or cutting blades. The output spindle 22 also includes a yoke or fork 26 spaced apart from the tool accepting portion 24 and having two arms 28 positioned on opposite sides of the spherical drive bearing 20. The fork 26 is configured to rotate about an axis A that is generally perpendicular to the longitudinal axis S of the motor shaft 18 by cyclic angular displacement of the fork about the axis A.
More specifically, as shown in FIG. 3, the eccentric motor shaft 18 is operated by the motor M (shown in FIG. 1) to translate the spherical drive bearing 20 in a circular path in a plane P1 which is arranged orthogonally to the longitudinal axis S of the eccentric motor shaft 18. As shown in FIG. 4, the travel of the spherical drive bearing 20 in the circular path or orbit periodically brings an outside surface 34 of the outer race 23 of the spherical drive bearing 20 into contact with an inside surface 36 of each of the arms 28 of the fork 26. A schematic drawing of the spherical drive bearing 20 in two positions superimposed onto one another is shown in FIG. 4 to illustrate contact of the outside surface 34 of the outer race 23 with the inside surface 36 of each of the arms 28. As a result of the contact with the spherical drive bearing 20, the fork 26 rotates about the axis A in an arced path 30 shown in FIG. 4 and FIG. 5. This arced path is contained within a lateral plane P2 shown in FIG. 3. Turning now to FIG. 5, the movement of the fork 26 in the arced path 30, is translated through the output spindle 22 to the tool or tool accessory coupled to the oscillating power tool 10.
The spherical shape of the spherical drive bearing 20 enables the fork 26 to move in this arced path 30 without interfering with the circular path of the spherical drive bearing 20 and enables the outside surface 34 of the outer race 23 of the spherical drive bearing 20 to slide and roll along the inside surfaces 36 of the arms 28. Additionally, the shapes of the spherical drive bearing 20 and the fork 26 translate the circular movement of the spherical drive bearing 20 in plane P1 into lateral movement of the fork 26 in plane P2 because the spherical drive bearing 20 does not engage the arms 28 of the fork 26 when moving upwardly and downwardly in the plane P1.
This conventional design results in wear and damage to the components of the oscillating power tool 10 and thereby reduced life of the tool. A number of issues arise due to the interaction of the components at the interfaces where the spherical drive bearing 20 contacts the arms 28 of the fork 26. Because the spherical outside surface 34 of the spherical drive bearing 20 is contacting planar inside surfaces 36 of the arms 28, the surface areas of the contact are concentrated to a single point on the inside surface 36 of each arm 28, which generates excessive heat during use of the tool 10. Additionally, enabling rotational movement of the spherical drive bearing 20 while the fork 26 maintains its rotational position results in sliding of the outer race 23 of the spherical drive bearing 20 at these interfaces between the outside surface 34 of the outer race 23 and the inside surfaces 36 of the arms 28. This sliding creates heat and wear on the surfaces 34, 36 of the interface which reduces the life of the parts of the tool 10.
Additionally, movement of the spherical drive bearing 20 in plane P1 relative to motion of the fork 26 in plane P2 results in upward and downward sliding of the spherical drive bearing 20 at these interfaces between the outside surface 34 of the outer race 23 and the inside surfaces 36 of the arms 28. While in theory the spherical drive bearing 20 would roll along the interface when in contact with the arms 28, in physical testing it is observed that the spherical drive bearing 20 intermittently contacts the arms 28 of the fork 26 and constantly changes direction of rolling, resulting in sliding. This upward and downward sliding generates heat and wear on the surfaces 34, 36 of the interface which contributes to the damage of the spherical drive bearing 20 and reduces the life of the tool 10. Furthermore, because the fork 26 is moving in the arced path 30, the movement of the fork 26 includes a lateral component as well as an axial component. The axial component of the movement of the fork 26 generates a moment in the spherical drive bearing 20 that introduces a load on the spherical drive bearing 20 in the direction of the longitudinal axis L.
Finally, with this conventional configuration, there must be some clearance between the arms 28 of the fork 26 and the spherical drive bearing 20 to enable the fork 26 to move only in the plane P2 and to ensure that the spherical drive bearing 20 does not engage the arms 28 of the fork 26 when moving upwardly and downwardly in the plane P1. This clearance results in impacting and banging of the fork 26 with the spherical drive bearing 20 which contributes to the load on the spherical drive bearing 20.
Accordingly, it can be seen that the conventional oscillating mechanism can have a deleterious impact on the life of the spherical drive bearing 20. The sources of this weakness include: a) the point of contact between the spherical drive bearing 20 and the arms 28 of the fork 26; b) the sliding of the outer race 23 of the spherical drive bearing 20 due to the relative rotation between the spherical drive bearing 20 and the fork 26; c) upward and downward sliding of the spherical drive bearing 20; and d) banging or impacting of the spherical drive bearing 20 due to necessary looseness of the interface.
Robustness, or more accurately, lack of robustness limits the size of the tool attachment and the operating conditions of the conventional oscillating power tool 10, which can ultimately limit performance. A larger tool attachment increases the load on the spherical drive bearing 20. An increase in the operating speed also increases the bearing load. This increased load forces limits to be placed on the size of the tool and on the operating speed of the tool. Consequently, there is a need for an oscillating mechanism that overcomes these problems and allows for higher “power” and performance operation of an oscillating tool.